OBJECTIVE: We aimed to examine the effect of emotion regulation training in patients with panic disorder (PD) by measuring heart rate variability (HRV). METHODS: Forty-eight patients with PD were randomly divided into emotion regulation group (n=25) and no-regulation group (n=23). Three five-minute ECG recordings were taken in the following states: 1) baseline, 2) while subjects viewed 15 aversive pictures (active stimulus), 3) resting state after aversive pictures (post-stimulus). The emotion regulation group briefly received acceptance technique training for five minutes before performing the experimental task. Spectral analysis measures included a high-frequency (HF; 0.15-0.4 HZ) component, a low-frequency (LF; 0.04-0.15Hz) component, and an LF/HF ratio. RESULTS: The mean change in LF/HF ratio from baseline to active stimulus was significantly lower in the emotion regulation group than in the no-regulation group (emotion regulation group, 0.13; no-regulation group, 2.31; t=-2.67; P<.05). CONCLUSION: This suggests that brief emotion acceptance training could decrease aversive stimulus-induced sympathetic hyperactivity in patients with PD.